1. Field of the Invention
The present invention relates to an insole having a shank comprising a fiber-reinforced resin sheet and a method of producing the same.
2. Description of the Prior Art
The shank put on the insole of a shoe maintains the shape of the shoe and functions as a spring during walking. The shank has an important influence upon the properties and durability of the shoes. Properties required for a shank are as follows.
(1) The shank should have a suitable bending rigidity.
(2) The shank should have a high destruction strength.
(3) The original state of the shank should be immediately restored if the shank is bent, and then released.
(4) The shank should be light in weight.
Generally, an insole element (this term being used to describe an insole before a shank has been put thereon), especially the rear half comprising the heel-nontread part-tread part, comprising press-board, wood, nonwoven cloth, cloth or leather impregnated with a binder has been molded with hardening by heat so as to form a curved surface which coincides with the shape of a shoe. Then, the rear-half of this insole element and a shank are fixed together to produce an insole.
Hitherto, iron or steel has been mainly used as raw materials for a shank. A shank made from iron or steel is difficult to comform to the curvature of a shoe last, and a two-step process which comprising preparing each of the shank and the insole element separately and unifying them has been employed. Therefore, it is very difficult to mold so that the face of the heel-nontread part-tread part of the insole element and the face of the shank have each the same curvature.